NAT Type Nightmare

[#1]

Im having a nightmare with NAT type for Black Ops on my Xbox 360!!
Ive checked all the previous threads and tried the solutions put forward but unfortunately to no avail.
Ive had Plusnet for 2 weeks.
Initially Black Ops multiplayer worked great for the first 24 hours. I could join games,i could enter games having been invited from online friends. Suddenly i cant join games.I can accept invites from friends on the game,i can join those games but my connection is really slow. Its unplayable. (My Xbox live works great by the way)
Heres what ive tried:
Ive tried port forwarding.Doesnt work. My Pnp is enabled.My extended firewall is disabled. Ive assigned Xbox live to the Xbox wireless thats detected on the router. Ive given the xbox a static IP.  Ive tried for 5 hours changing my settings but nothing is working!
Please could someone help me??!! 
Thanks for reading.
Mark

[#2]

Hi Mark
Keep the xbox on a static IP, and place the xbox in a DMZ (you havent said you've tried this?)
What router are you using?
DMZ is like opening ALL ports (disables the firewall for that IP)

Have you had trouble with other games? also is the Plusnet Firewall switched off (get to it via the member portal)
Regards

[#3]

if you have a thompson 585 router forward your ports heres how to do it
http://portforward.com/english/routers/port_forwarding/Thomson-Alcatel/SpeedTouch585/Call_of_Duty_-_...

[#4]

With respect SilentBoBuk..
the OP would be better placing the xbox in a DMZ, it will mean that they do not have to open ports for every new game etc.
Set and forget

[#5]

Yeah thought that would help if he's having problems its normaly best to port if you wanna play zombies on black ops as the dmz doesnt work all the time for it

[#6]

I too have the same problem.
I've tried the suggested port forwarding from Xbox.com and assigned the Xbox a static IP address, but the NAT is still STRICT.
btw, the link above about Black Ops appears to be for the PC version. I think you should only need to do the set up once for the Xbox and it will cover all Xbox Live communication.
I'm using a Thomson Gateway GT585v8 router, which doesn't appear to have any DMZ options.
Does anyone else out there have this router and use it with an Xbox and have an OPEN NAT?

[#7]

There is a DMZ option on that router which is difficult to find it took me ages. I'm at work at the minute so not sure but off the top of my head I think you go to devices, then at the bottom of the page where it says pick a task it will say something like "assign a public ip to a device" then select then select the XBOX from your devices which needs to be static and save/re-boot the router.
It is a bit vague but if you read the description it says something like this will assign your public ip to a device then in brackets (DMZ) if you can't find it give me a shout later when I get home.